Cable containing optical transmission elements and method for the production thereof

ABSTRACT

A cable, and process for manufacture thereof, containing optical transmission elements. The cable having the following characteristics: a central element stretching in the direction of the cable longitudinal axis, where the central element has at least one slot open to the outside and where the slot runs on the outside of the central element in a helix or screw-like manner, with periodically changing rotation direction; several optical fiber ribbons arranged inside the slot in a stack, situated one above the other, where an additional equal lay stranding is applied to the SZ-stranding imposed by the slot path; and a single or multi-layer jacket surrounds the central element.

FIELD OF THE INVENTION

The present inventions relate generally to the field of fiber opticcables and manufacturing methods thereof and, more specifically, toslotted core fiber optic cables.

BACKGROUND OF THE INVENTION

The slotted core cable developed more than 30 years ago distinguishesitself especially for its high tensile and compression resistance andits compact construction, in spite of the large number of the opticalfibers arranged in the slots of the central element. Optical cables ofthis kind are f.e. described in U.S. Pat. Nos. 5,517,591 and 5,199,094.

An essential component of the slotted core cable is the cylindricalcentral element, on whose jacket several slots are located, each of themopen to the outside, in the form of a helix or spiral, if need be withperiodically changing rotation direction. The process for themanufacture of such a central element can be found in U.S. Pat. Nos.4,997,258 and 5,380,472.

The invention concerns a cable containing an optical transmissionelement with a central element and optical fiber ribbons arranged in theslots of the central element. The invention also concerns a process forthe manufacture of such a cable.

In order to increase the number of the optical fibers (LWL) serving asoptical transmission elements, consisting of a glass core (refractiveindex n_(x)), a glass jacket (refractive index n_(m)<n_(x)) and a singleor multi-layer protective covering (coating) in the slotted core cable,typically 8-16 optical fibers (LWL) are mechanically combined into aribbon, and several of these ribbons are inserted into the slot of thecentral element one above the other in the form of a stack. U.S. Pat.Nos. 4,997,255 and 5,380,472 are especially relevant here. If the slotin the outer area of the central element describes a helix, whoserotation direction changes periodically, the optical fiber ribbons aretwisted respectively, and thus subjected to a so-called SZ-stranding.The torsion thus produced in the optical fiber ribbons induces elasticforces, which cause the optical fiber ribbons in the slot to assume apreferred direction. Due to this alignment of the optical fiber ribbonsin the slot the cable has two developed main axes with different bendingbehavior. This results in the following disadvantages:

-   -   a) The lengths of the individual optical fiber ribbons are not        equally distributed onto the areas subjected to strain during        bending of the cable. Especially the outer optical fiber ribbons        of the stack are subject to high mechanical stresses, so that        their signal attenuation is significantly increased due to micro        and macro-bending.    -   b) The preferred alignment of the optical fiber ribbons leads to        a mechanically unstable configuration at small bending radii.        During bending of the cable, this can lead to spontaneous change        in the order of the optical fiber ribbons in the cable. This        also increases attenuation.

SUMMARY OF THE INVENTIONS

It is the objective of this invention to create a cable containing anoptical transmission element, especially an SZ-stranded slotted corecable, with an improved bending behavior in relationship to signalattenuation. The components of the cable should be synchronized to eachother or work together in such a way, that the cable has almost the sameflexibility in all bending directions.

This objective is achieved by a cable containing an optical transmissionelement with the following characteristics:

-   -   it contains a central element stretching along the direction of        the longitudinal cable axis, where the central element shows at        least one slot open to the outside, and the slot runs on the        outside of the central element helically or screw-like, with        periodically changing rotation direction;    -   several optical fiber ribbons, arranged over each other in the        form of a stack, serve as transmission elements, where an        additional equal lay stranding is added to the SZ-stranding        caused by the slot rotation;    -   a single or multi-layer jacket surrounds the central element.

A process for the manufacture of such a cable containing an opticaltransmission element consists of the execution of the following steps:

-   -   provision of a central element, where the central element shows        at least one slot open to the outside and the slot running on        the outside of the central element helically or screw-like, with        a changing rotation direction;    -   payoff of the optical fiber ribbons serving as optical        transmission elements from respective storage reels, combining        the optical fiber ribbons into a stack;    -   insertion of the ribbon stack rotating around its longitudinal        axis with a constant speed into the slots, and    -   application of a single or multi-layer jacket.

The dependent claims give constructions and advantageous developments ofthe cable or the manufacturing process, respectively.

The preferred construction of the optical fiber ribbons in the slots canbe avoided, by adding an additional stranding to the SZ-stranding causedby the rotation of the slots. This results in the following advantages:

-   -   the cable does not have a well-defined main axes with different        bending behavior;    -   the flexibility of the cable is clearly improved;    -   for all optical fiber ribbons of the stack, the length of the        tensile stressed segments always corresponds to the length of        the compression stressed segments;    -   during bending of the cable, no spontaneous rearrangement of the        optical fiber ribbons in the slot occurs.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

In the following the invention is more clearly explained by means ofconstruction samples and their respective drawings. Shown are:

FIG. 1 central element with different slot arrangements, which give theinserted ribbons an S-stranding (FIG. 1 a), an SZ-stranding (FIG. 1 b)and a Z-stranding;

FIG. 2 the projection of a selected slot onto the cross-section surfaceof the central element a various points of the cable longitudinal axis(=longitudinal axis of the central element) between adjacent reversalpoints;

FIG. 3 the projection shown in FIG. 2 of the slot on the cross-sectionsurface of the central element, as well as the two orthogonal bendingaxes;

FIG. 4 the graph of the Bessel function J₀(Φ₀/2) of zero power and itszero points corresponding to the ideal reversal angles Φ₀;

FIG. 5 the location relationship of the curving of the sphericalcurvature along the cable axis connecting the center points of the slot;

FIG. 6 the location relationship corresponding to FIG. 5 of the curvingradius along the cable axis;

FIG. 7 the projection of the curving vector of the spherical curvatureconnecting the center points of the slot onto the cross-section surfaceof the central element at various points of the cable axis betweenadjacent reversal points;

FIG. 8 the location relationship of the angle enclosed by the curvingvector and the radial unit vector at various points of the cable axisbetween adjacent reversal points;

FIG. 9 an optical fiber ribbon in cross-section;

FIG. 10 several optical fiber ribbons combined into a stack incross-section;

FIG. 11 the location of the ribbon stack within the slot, at variouspositions between adjacent reversal points;

FIG. 12 the shear or elongation energy accumulating in the SZ-strandedoptical fiber ribbons during a bending of the central element around they-axis relative to the bending radius;

FIG. 13 the location of the ribbon stack within the slot before andafter a bending of the central element around the x-axis;

FIG. 14 the shear or elongation energy accumulating in the SZ-strandedoptical fiber ribbons of the stack during a bending of the centralelement around the x-axis in relationship to bending radius;

FIG. 15 the elongated ribbon stack and the ribbon stack twisting aroundits longitudinal axis at an angle of 2π per SZ lay length;

FIG. 16 the location of the SZ-stranded of a ribbon stack additionallytwisted around its longitudinal axis within the slot at various pointsof the cable longitudinal axis between adjacent reversal points, in casethe ribbon stack inserts rotating (FIG. 16 a) or straight, respectively(FIG. 16 b);

FIG. 17 the shear or elongation energy accumulating in the SZ-strandedoptical fiber ribbons of the stack which are additionally twisted aroundtheir longitudinal axis during a bending of the central element aroundthe y-axis in relationship to the bending radius;

FIG. 18 the shear or elongation energy accumulating in the SZ-strandedoptical fiber ribbons of the stack which are additionally twisted aroundtheir longitudinal axis during a bending of the central element aroundthe x-axis in relationship to the bending radius;

FIG. 19 the ribbon payoff and the insertion tool of a line for themanufacture of an SZ-stranded slotted core cable with additional lay;

FIG. 20 a construction sample of a slotted core cable in cross-section;and

FIG. 21 the spatial path of the SZ-stranded ribbon stack provided withan additional stranding (torsion at 2π/S) between adjacent reversalpoints.

DETAILED DESCRIPTION OF THE INVENTIONS

A) The Central Element

The path of the slots in the central element determines the type ofstranding of the optical fiber ribbons inserted in the slots andfollowing the slot strand. Basically, there is a normal stranding withequal lay (S- or Z-stranding) and the so called reverse lay(SZ-stranding). The central elements ZE effecting the respectivestranding of the optical fiber ribbons are shown in perspective in FIG.1. The 8 slots K of the cylindrical central element ZE shown in FIG. 1 aeach describe a helix or spiral (S-stranding of the optical fiberribbons) turning left in the direction of the cable longitudinal axis,i.e. the longitudinal axis of the central element ZE, the slots K of thecentral element ZE shown in FIG. 1 b a helix or spiral (Z-stranding ofthe optical fiber ribbons) turning right in the direction of the cablelongitudinal axis, i.e. the longitudinal axis of the central element ZE.In order to subject the optical fiber ribbons to an SZ-stranding, theslots K depicted in FIG. 1 b must show the nearly harmonic path (sine orcosine) depicted in FIG. 1 b on the periphery of the central element.This path happens by changing the rotation direction of the helix f.e.after a certain number N of rotations, maintaining this rotationdirection for the following N-rotations, and then again proceeding inthe original rotation direction. Therefore S-stranded and Z-strandedsegments (“helicals”) follow periodically on the jacket surface of thecentral element. Between adjacent segments of “equal lay stranded”segment there is always a transition area described as “reversal”.

b) Coordinate System and Parameterization

For the following discussion, the examination of the f.e. eight slots Kpresent in the cylindrical central element ZE and mostly parallelrunning is sufficient. In FIG. 2 a projection of such a slot at variouspoints of the cable longitudinal axis between successive reversal pointsin the xy-level of the accompanying coordinate system is depicted. Thelocation of the chosen slot at the two reversal points (slotcross-sections K_(S) and K_(R) as well as the location of the slot inthe center of the equal lay segments (slot cross-section K_(H)) areemphasized. The dash line should symbolize the location of the slotcenter at the other points of the examined axis segment. The arrowdesignated as D_(S) indicated the rotation direction of the slot path.

Due to the geometry of the central element ZE a cylindrical coordinatesystem for mathematical description of the slot path is available. Thex-axis defining the angle zero point of the coordinate system runspreferably through the center of the slot cross-section K_(H) assignedto the helical, so that the slot cross-sections K_(R) and K₃ are locatedsymmetrically to the x-axis. The angle Φ describing the azimuthallocation of the slot in the y-level has the value Φ_(R)=Φ₀/2, Φ_(H)=0and Φ₃=Φ₀/2 for the slot segments K_(R), K_(N), and K_(H). Thelongitudinal axis of the central element ZE forms the z-axis of thecoordinate system.

In the construction sample shown, the so-called reversal angle Φ₀ isless than 360°, i.e. the slot strand rotating to the left does notrotate completely on the jacket surface of the central element ZEbetween subsequent reversal points.

The following examines more closely not the real path of the spatiallyelongated slot which is difficult to describe mathematically, but onlythe spherical curve connecting the center of the slot and described bythe tip of vector Z. The vector T swinging periodically in an angle Φwith the maximum values Φ_(max)=±Φ₀/2 around the x-axis has a constantlength of r₀, so that the parameterization of the spherical curvatureconnecting the centers of the slot is as follows in cylindercoordination: $\begin{matrix}{{T(z)}_{r\quad\phi} = \left( {{\frac{\Phi_{0}}{2} \cdot \cos}{\,_{z}^{r_{0}}\left( {{\frac{z}{S} \cdot 2}\quad\pi} \right)}} \right)} & (1)\end{matrix}$where r₀, Φ₀, S have the following meaning:

-   r₀: constant radial distance to z-axis-   Φ₀: reversal angle-   S: laylength (double the axial distance of adjacent reversal points)    With x=r₀cos (Φ) and y=r₀sin (Φ) the curve can be depicted in    cartesian coordinates as: $\begin{matrix}    {{T(z)}_{xy} = \begin{bmatrix}    {r_{0} \cdot {\cos\left( {{\Phi_{0}/2} \cdot {\cos\left( {{\frac{z}{S} \cdot 2}\quad\pi} \right)}} \right)}} \\    {r_{0} \cdot {\sin\left( {{\Phi_{0}/2} \cdot {\cos\left( {{\frac{z}{S} \cdot 2}\quad\pi} \right)}} \right)}} \\    z    \end{bmatrix}} & (2)    \end{matrix}$

The spherical curvature connecting the slot center points, alsodesignated as stranding curvature in the following, is thereforedesignated as one-dimensional in z, in cylinder coordinates as well asin Cartesian coordinates.

c) Ideal Reversal Angle Φ₀

The reversal angle Φ₀ describes the azimuthal distance of the slotcross-sections K_(S) and K_(R) assigned to adjacent reversal points inthe xy-level. In order to guarantee the flexibility of the centralelement ZE and thus also of the cable, equal length of an optical fiberhas to be in the compression and tensile stress areas of the cableduring equal bending around a given axis. This condition is always metfor cables stranded with equal lay, but for SZ-stranded cables only fordiscrete values of the reversal angle Φ₀.

Now the bending of the central element ZE around the x-axis as bendingaxis as depicted in FIG. 3 is examined. In this case, independent fromthe reversal angle Φ, equal length of the stranding curvature on thepositive and negative segment of the y-axis is located, so that thelength of the compression stressed fiber segments corresponds to thelength of the tension stressed fiber segments.

A bending of the central element ZE around the y-axis has theconsequence, that the relationship of the length of the strandingcurvature located in the positive segment of the x-axis and the lengthof the stranding curvature located in the negative segment of the y-axisconstantly changes relative to the reversal angle Φ. If the reversalangle Φ is larger than Φ=180°, the total length of the strandingcurvature is located in the positive area of the x-axis, i.e., accordingto the bending direction totally in the compression or tension stresssegment of the cable. With increasing reversal angles 180°<Φ<360° theunequal weight between the lengths of the stranding curvature located inthe positive and negative segments of the x-axis continually andequalizes at the desired ideal reversal angle Φ₀.

The condition, where the length of the stranding curvature in thepositive segment of the x-axis has to equal the length of the strandingcurvature in the negative segment of the x-axis leads to the requirement$\begin{matrix}{{\int_{0}^{s}{{T(z)}_{x}{\mathbb{d}z}}} \equiv 0} & (3)\end{matrix}$where T_(x)(z) designates the x-component of the vector T(z).Considering the parameterization given in equations 1) and 2), theequation (3) can be formed into a definition equation for the idealreversal angle Φ₀. $\begin{matrix}\left. {{\int_{0}^{s}{{r_{0} \cdot {\cos\left( {\frac{\Phi_{0}}{2} \cdot {\cos\left( {{\frac{z}{S} \cdot 2}\quad\pi} \right)}} \right)}}{\mathbb{d}z}}} \equiv 0}\Leftrightarrow{{\frac{S}{2\quad\pi} \cdot {\int_{0}^{2\quad\pi}{{r \cdot {\cos\left( {\frac{\Phi_{0}}{2} \cdot {\cos(\varphi)}} \right)}}{\mathbb{d}\varphi}}}} \equiv 0} \right. & (4)\end{matrix}$

The integral corresponds to the Bessel function J₀(Φ₀/2) of zero power,whose zero points correspond to the desired ideal reversal angle.

FIG. 4 shows the value of the integral I(Φ₀) calculated by means ofnumerical integration for reversal angles in the range of 0°≦Φ₀≦1200°.The absolute value of the integral here depends among others on the laylength, set f.e at 500 mm. Since the lay length S does not influence thelocation of the zero points, the optimum reversal angles are Φ₀=275.5°,632.6°, etc. A good approximation of possible reversal points Φ₀ arelocated on the straight line given byΦ₀=359,29°·n−85.223°  (5)d) Curving, Curving Radius and Curving Direction of the StrandingCurvature

For the central elements ZE depicted in FIGS. 1 a and 1 b the curving aswell as the curving radius of the space curvatures describing each slotpath are constant and the curving direction, i.e. the vector of thecurvature normal lines in the direction of the curvature center, arepointing to the inside towards the longitudinal axis of the centralelement ZE (S- or Z-stranding). This basically distinguishes it from thespace curvature assigned to the slot path of the SZ-stranded centralelement ZE and described by the tip of the vector T, whose curving,curving radius and curving direction show a relationship to location.

The location relationship looked for can be calculated analytically ornumerically by means of the above mentioned parameterization, where thecurving and the curving radius qualitatively show the path along thecable longitudinal axis (z-axis) within a segment with a length of S=500mm as depicted in FIG. 5 or FIG. 6, respectively. In the equal lay area,there is maximum curving, the curving radius is therefore at a minimum.In the axis segments between two equal lay areas containing the“reversal point”, it is the exact opposite, i.e. the curving is at aminimum, while the curving radius takes on a maximum value.

FIG. 7 schematically depicts the projection of curving vector krepresenting the curving direction, also deducted from the abovementioned parameterization, at various points of the z-axis onto thecross-section of the central element ZE. It is shown that the curvingvector k is pointing tangentially to the outside at the reversal pointsand radially to the inside in the equal lay areas. When applying theangle a enclosed by the curving vector k and the radial unit vector 3,in relationship to the z-coordinate, the function shown in FIG. 8 is theresult.

e) Optical Fiber Ribbon and Ribbon Stack

The light transmitting part of the cable is also subject to the locationrelationship of the curving and the curving direction given by the slotpath in the central element ZE.

If this is a single optical fiber consisting of a glass core, a glassjacket and a normally multi-layer protective covering (coating), thewound slot path causes no problems. Due to its high flexibility andradial symmetry the optical fiber can easily follow the stranding curve.

An entirely different behavior is shown by the optical fiber ribbon LB,depicted in cross-section in FIG. 9, which f.e. contains 16 opticalfibers LW1-LWn, aligned relative to their longitudinal axes and beingheld together mechanically by a plastic jacket BC. The optical fiberribbon LB has two main axes with different bending behavior, where theso-called weak bending axis (ribbon easily bendable) is orientedvertically to the ribbon longitudinal axis and is located in the levelfixed by the ribbon LB; and the stiff bending axis (ribbon difficult tobend),which is vertical to the ribbon longitudinal axis as well as theweak bending axis. If such a ribbon is inserted into a slot showing theabove mentioned curvature path, a very complex state of stress iscreated.

A behavior similar to ribbon LB is shown in the ribbon stack BS shown incross-section in FIG. 10. In the construction sample shown, the stack BSconsists of five individual ribbons LB1-LB5, situated above one anotherand being parallel, each of them having four optical fibers serving assignal conductors. The stack BS has two main axes with different bendingresistance just like the individual ribbons LBi. In FIG. 10, the weakbending axis is designated as k, the stiff bending axis as 1.

In order to minimize the shear and normal forces (tensile andcompression forces) in a straight cable, the light transmitting elementsare inserted into a sufficiently large slot allowing free rotation ofthe optical fiber ribbons LBi. Due to their stiffness the optical fiberribbons LBi perform a back rotation in the slot, which is countered bythe torsion around the ribbon longitudinal axis which is forced upon itby the slot path. This back rotation leads to a preferred alignment ofthe ribbons LBi in the slot in such a way, that the stiff bending axisof the ribbons LBi points nearly in the direction of the y-axis in thechosen coordinate system. As shown in FIG. 11, the ribbon stack BS atthe helical “stands” therefore vertically in the slot, while taking arather “lying-down” position in the two adjacent reversal points. Due tothis back rotation only the middle ribbon LB (ribbon No. 3) of the stackBS shows the ideal reversal angle Φ₀. For the ribbons No. 1 and 2 thereversal angle is greater, for the ribbons No. 4 and 5 it is smallerthan the ideal value. As explained above, the two outer ribbons (ribbonsNo. 1/2 and No. 4/5) are therefore not completely stranded in thisconfiguration, i.e. in the case of a bending of the cable they aresubjected to compression and tensile stresses leading to attenuationincreases.

FIG. 12 shows the sum of compression and elongation energy relative tothe bending radius building up in the individual ribbons during bendingof the central element ZE around the y-axis. Due to the incompletestranding the uppermost and lowest ribbons (ribbon No. 1 and 5) arestressed the most in the stack; the middle ribbon (ribbon No. 3) theleast.

During a bending of the central element ZE around the x-axis, theribbons LBi are stressed over their stiff bending axis (axis 1 in FIG.10). Since the ribbons LBi are loosely arranged in the slot, they canavoid this stress by a rotation around the z-axis. As indicated in FIG.13, the ribbons LBi, beginning from the situation shown in the left partof FIG. 13, take up finally the position, shown in the right part ofFIG. 13 within the slot at the adjacent reversal points and the helicallocated between them.

In the corresponding energy diagram (see FIG. 14), instability isdetected for bending radii smaller than 0.4 mm, i.e. the built-upmechanical tension is removed by a spontaneous rotation of the ribbonsBLi around the z-axis. This disturbs the arrangement of the ribbons LBiin the stack BS, which in turn leads to attenuation increase.

f) Twisted and Straight Insertion of Ribbons into the Slot

The above described disadvantages are based on the back rotationbehavior of the ribbons LB and the resulting preferred alignment of theribbon stack BS in the slot. The preferred alignment can be kept bylayering an equal length stranding over the torsion (SZ-stranding)inflicted on the ribbon LB by the slot path. This can be done by anadditional synchronous rotation of the ribbon stack BS around itslongitudinal axes, where the rotation angle is 2π it per SZ lay lengthS.

During stranding with additional lay the type of insertion of theribbons LB into the slot K is of great importance. There is adistinction between “twisted” insertion and “straight” insertion; theseconcepts have the following meaning:

Twisted Insertion

The ribbon stack BS is arranged in the slot K at the helicals in such away, that the weak bending axis k of the stack BS or the ribbons LBi,respectively, and the x-axis of the previously defined coordinate systemrun parallel, or the weak bending axis k of the stack BS is standingvertically on the level defined by the floor of the slot (the stack BSlies at the helical of the slot; compare FIG. 16 a).

Straight Insertion

The stiff bending axis 1 of the ribbon stack BS or the ribbons BLi,respectively, and the x-axis run parallel (the stack “stands” at thehelical in the slot; compare FIG. 16 b).

Both insertion types are differentiated not in regard of the torsionaround the stack longitudinal axis occasioned by the additional lay, butsolely in regard to the orientation of the ribbon stack BS within theslot at the helicals. It can be seen at once in FIG. 16, that allribbons LBi of the stack BS only show the ideal reversal angle Φ₀, whenthe stack BS is inserted “twisted”.

FIGS. 17 and 18 depict a ribbon stack BS, corresponding to the energydiagrams in FIGS. 12 and 14, being inserted twisted, SZ-stranded andadditionally twisted around its longitudinal axis (2π per lay length S),where FIG. 17 depicts the stress of the ribbons LBi during bending ofthe central element ZE around the y-axis, and FIG. 18 the stress of theribbons BLi during bending of the central element ZE around the x-axis.All relevant parameter for the calculation of the energy levels wereunchanged except of the equal lay stranding applied over theSZ-stranding.

Due to the additional stranding applied to the optical fiber ribbons LB,they behave nearly identical during bending around an orthogonal axis(compare the path of the curves and ordinate values depicted in FIGS. 17and 18), i.e. the bending behavior of the ribbons is relative todirection and therefore nearly ideal. The energy levels assigned to theindividual ribbons are very close together within the examined area ofthe bending radii, which indicates an equal stress of the ribbons LB.The stress is also comparatively small, since the energy level assignedto the smaller bending radii (r<0.25 m) is only slightly higher than thebeginning level. There is also no instability in any of the energydiagram.

g) Process for the Manufacture of an SZ-stranded Slotted Core Cable withAdditional Lay

As has just been explained, the preferred alignment of the ribbons LB inslot K can be offset by an equal lay applied over the SZ-stranding. Forthe manufacture of such a cable, the device known from (3) and clearlydescribed there, for the manufacture of an SZ-stranded slotted corecable has to be modified. Since the modification concerns only theribbon payoff and the insertion tool normally designated as “finger”,the other components and elements of the production line can be ignoredin the following.

As shown schematically in FIG. 19, the ribbon payoff in the productionline assigned to a slot K in the central element ZE in the constructionshown consists of a total of 5 storage reels (VS1-VS5) fastened to aframe not shown and each being rotated around their longitudinal axis.The ribbons LB1-LB5 payed off these storage reels VS1-VS5 are broughtinto proximity to each other, perhaps threaded into a guide tube andinserted by a longitudinally stretched finger F with f.e. O-like orcircular cross-section as stack BS in the corresponding slot K of thecentral element ZE (see enlarged segment in the right part of FIG. 19).The central element ZE and the steel wire S guaranteeing the tensionresistance of the cable move with constant line or payoff speed VL alongthe z-axis. At the same time, the steel wire S, the central element ZE,the finger F and the ribbon payoff, designated by double arrows performa harmonic oscillation in the stranding angle φ₀ around the z-axis.

In order to produce the additional lay of the ribbons LB, all storagereels VS1-VS5 rotate during payoff synchronously with the constant anglespeedω_(s)=(2π/S)·v_(L)  (6)where S and v_(L) are:

-   S: SZ lay length-   v_(L): payoff speed    around a rotation axis standing vertical on the longitudinal axis of    the storage reels VS1-VS5. With a payoff speed of typically v_(L)=20    m/min and a lay length of f.e. S=0.5 m the angle speed ω_(s) of the    storage reels VS1-VS5 are ωs=4 s⁻¹.

After the simultaneous insertion of each ribbon stack BS in the f.e. 8slots, the central element ZE is surrounded by a so-called swell fleeceor a webbing and subsequently provided with a single or multi-layerplastic jacket made of PE or PP. The swell fleece is supposed to sealthe slots to the outside, in case of water penetration into the cablecore due to a damaged jacket. Additionally, the swell fleece avoids thespreading of the water in the inside of the cable.

As shown in FIG. 20, the cable OK produced by such a process can consistf.e. of a compression resistant element S (steel wire, glass fiberreinforced plastic rod, ARP (aramid reinforced plastics) rod) aspoke-like PE central element ZE showing six slots K, a swell fleece QFor a determination and single layer PE outer jacket MA. The measurementsof the slots K are done in such a way, that the ribbon stack BS canrotate freely in its slot K. The slot K can show a trapezoid or a nearlycircular cross-section. The ribbon stack BS being inserted twisteddescribes the space curvature between adjacent reversal points given bythe path of the slot in central element ZE, as shown in FIG. 21.

1. A cable containing optical transmission elements comprising: a central element (ZE), the central element (ZE) stretching in the direction of a cable longitudinal axis (z), where the central element (ZE) has at least one slot (K) open to the outside and where the slot (K) runs on the outside of the central element (ZE) in a SZ orientation having a periodically changing rotation direction; a plurality of optical fiber ribbons (LB), the plurality of optical fiber ribbons (LB) being arranged inside the slot in a ribbon stack, where an additional equal lay stranding is applied to the SZ-stranding imposed by the slot path; and a jacket surrounds the central element ZE.
 2. The cable according to claim 1, wherein the equal lay stranding is formed by the continuous rotation of the plurality of optical fiber ribbons (LB) about a ribbon stack longitudinal axis, where the rotation about the ribbon stack longitudinal axis is about 360° per lay length S of the slot (K) with the SZ orientation.
 3. The cable according to claim 2, wherein the ribbon stack (BS) at locations near about the center of subsequent reversal points is arranged in the slot (K) in such a way, that axis (K) of the optical fiber ribbons (LB), which is less stiff relative to bending behavior, is essentially vertical to the slot floor.
 4. The cable according to claim 1, wherein a space curvature connecting the center points of the slot along the cable longitudinal axis being given by ${T(z)}_{xy} = \begin{bmatrix} {{ro} \cdot {\cos\left( {{\Phi_{0}/2} \cdot {\cos\left( {{\frac{z}{S} \cdot 2}\quad\pi} \right)}} \right)}} \\ {{ro} \cdot {\sin\left( {{\Phi_{0}/2} \cdot {\cos\left( {{\frac{z}{S} \cdot 2}\quad\pi} \right)}} \right)}} \\ z \end{bmatrix}$ and that a projection of a vector, originating from the cable longitudinal axis, pointing to the outside to the center of the slot sweeping over the angle Φ₀ onto a level vertical to the cable longitudinal axis between subsequent reversal points, where the angle Φ₀ of the condiction ∫₀^(s)T(z)_(x)𝕕z ≡ 0 is sufficient.
 5. The cable according to claim 4, wherein the angle Φ₀ is selected from one of the values Φ₀=275.5°±0.5° and Φ₀=632.5°±0.5°.
 6. The cable according to claim 1, wherein the central element (ZE) includes a plurality of slots (K).
 7. The cable according to claim 1, wherein the cable includes a wrapping or webbing which swells when water penetrates, thereby inhibiting the migration of water along the cable.
 8. The cable according to claim 1, wherein the central element (ZE) includes a core element (S).
 9. A process for the manufacture of a cable containing optical transmission elements comprising the following steps: providing a central element (ZE), the central element (ZE) having at least one slot (K), wherein the slot (K) runs at the outside of the central element (ZE) in a S-Z orientation having a changing rotational direction, paying off a plurality of optical fiber ribbons serving as transmission elements from a plurality of respective reels, combining the plurality of optical fiber ribbons into a ribbon stack (BS), rotating the ribbon stack (BS) with a constant angular speed about a ribbon stack longitudinal axis, inserting the ribbon stack (BS) rotating with a constant angular speed into the slot (K), and extruding a jacket (MA) about the central element (ZE).
 10. The process according to claim 9, wherein the ribbon stack (BS) rotates with angular speed of about ω₃=(2π/S)·v_(L) about the ribbon stack longitudinal axis during insertion, where the value S designates the lay length of the SZ-stranding forced onto the ribbon stack (BS) by the path of the slots (K) and the value v_(L) designates the payoff speed of the central element (ZE).
 11. The process according to claim 10, wherein each of the plurality of respective reels rotates with an angular speed of about ω_(s) around a second axis enabled by a rotating axis vertical to the payoff of the respective optical fiber ribbon.
 12. The process according to claim 10, wherein a tool (F) is used for guiding the ribbon stack and inserting it into the slot (K) and tool (F) rotates with the angular speed of about ω₃=(2π/S)·v_(L). 